Long survival in patients with leigh syndrome and the m.10191T>C mutation in MT-ND3 : a case report and review of the literature

Mitogenome-wide association study on body measurement traits of Wenshang Barred chickens

Mitochondria are best known for synthesizing ATP through the tricarboxylic acid cycle and oxidative phosphorylation. The cytoplasmic mitochondrial DNA (mtDNA) is important for maintaining the function. This study was designed to reveal the effect of mtDNA on chicken body measurement traits (BMTs). A population of 605 Wenshang Barred chickens were recorded BMTs, including body slope length, keel length, chest width, etc. The single-nucleotide polymorphisms (SNPs) of their mitogenomes were detected by PCR amplification and DNA sequencing. Totally 69 mutations in mitogenome were discovered, including 18 in noncoding region and 51 in coding region. By multi-sequence alignment and haplotype construction, the chickens were clustered into eight haplotypes and further three haplogroups. The association between BMTs and mtDNA SNPs, haplotypes and haplogroups were analyzed in the linear model by ASReml, respectively. Among them, the SNP mt11086 T/C in ND3 was found to significantly affect chest dept (p < .05) and was highly conservative by phylogenetic conservation analyses, which reflected the genetic effect on body size and growth of chickens. No significant association between the mitochondrial haplotypes or haplogroups and BMTs was found. The polymorphic site reflecting body size could be put into chicken breeding programs as the genetic marker.

Leigh-Like Syndrome With a Novel, Complex Phenotype Due to m.10191T>C in Mt-ND3

Leigh-like syndrome (LLS) due to the variant m.10191T>C in ND3 with a number of new phenotypic traits has not been published. In this case report, a 32-year-old woman diagnosed with Leigh-like syndrome presented with a complex novel, progressive, multisystem phenotype, manifesting in the brain (mild cognitive impairment, seizures, choreoathetosis, pseudotumor cerebri, hypersomnia, symmetric pallidal hypointensities, panda sign, calcifications, dysphagia), endocrine organs (empty sella syndrome, hypocorticism, hypoaldosteronism, hypogonadism), hematopoietic system (anemia, lymphocytosis), immune system (lymphocytosis, hypogammaglobulinemia), gut (reflux, diarrhea), kidneys (renal insufficiency, renal tubular acidosis, nephrolithiasis), muscles (myopathy, exercise intolerance, easy fatigability), peripheral nerves (small fiber neuropathy, dysautonomia), connective tissue (hyperlaxity of joints, bruising), and bones (scoliosis, Chiari malformation). A genetic workup revealed the known pathogenic variant m.10191T>C in ND3, which was also carried by the patient’s mother. This case demonstrates that the m.10191T>C variant in ND3 can phenotypically manifest with multisystem disease and that this disease is responsive to symptomatic treatment and application of additional compounds.

Association Between Epilepsy and Leigh Syndrome With MT-ND3 Mutation, Particularly the m.10191T>C Point Mutation

Background and Purpose: Recent advances in molecular genetic testing have led to a rapid increase in the understanding of the genetics of Leigh syndrome. Several studies have suggested that Leigh syndrome with MT-ND3 mutation is strongly associated with epilepsy. This study focused on the epilepsy-related characteristics of Leigh syndrome with MT-ND3 mutation identified in a single tertiary hospital in South Korea. Methods: We selected 31 patients with mitochondrial DNA (mtDNA) mutations who were genetically diagnosed with mtDNA-associated Leigh syndrome. Among them, seven patients with MT-ND3 mutations were detected. We reviewed various clinical findings such as laboratory findings, brain images, electroencephalography data, seizure types, seizure frequency, antiepileptic drug use history, and current seizure status. Results: The nucleotide changes in the seven patients with the Leigh syndrome with MT-ND3 mutation were divided into two groups: m.10191T>C and m.10158T>C. Six of the seven patients were found to have the m.10191T>C mutations. The median value of the mutant load was 82.5%, ranging from 57.9 to 93.6%. No particular tendency was observed for the first symptom or seizure onset or mutant load. The six patients with the m.10191T>C mutation were diagnosed with epilepsy. Three of these patients were diagnosed with Lennox-Gastaut syndrome (LGS). Conclusion: We reported a very strong association between epilepsy and MT-ND3 mutation in Leigh syndrome, particularly the m.10191T>C mutation. The possibility of an association between the epilepsy phenotype of the m.10191T>C mutation and LGS was noted.

Mutational Analysis and mtDNA Haplogroup Characterization in Three Serbian Cases of Mitochondrial Encephalomyopathies and Literature Review

Mitochondrial encephalomyopathies (MEMP) are heterogeneous multisystem disorders frequently associated with mitochondrial DNA (mtDNA) mutations. Clinical presentation varies considerably in age of onset, course, and severity up to death in early childhood. In this study, we performed molecular genetic analysis for mtDNA pathogenic mutation detection in Serbian children, preliminary diagnosed clinically, biochemically and by brain imaging for mitochondrial encephalomyopathies disorders. Sanger sequencing analysis in three Serbian probands revealed two known pathogenic mutations. Two probands had a heteroplasmic point mutation m.3243A>G in the MT-TL1 gene, which confirmed mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode syndrome (MELAS), while a single case clinically manifested for Leigh syndrome had an almost homoplasmic (close to 100%) m.8993T>G mutation in the MT-ATP6 gene. After full mtDNA MITOMASTER analysis and PhyloTree build 17, we report MELAS' association with haplogroups U and H (U2e and H15 subclades); likewise, the mtDNA-associated Leigh syndrome proband shows a preference for haplogroup H (H34 subclade). Based on clinical-genetic correlation, we suggest that haplogroup H may contribute to the mitochondrial encephalomyopathies' phenotypic variability of the patients in our study. We conclude that genetic studies for the distinctive mitochondrial encephalomyopathies should be well-considered for realizing clinical severity and possible outcomes.

Clinical application of sequencing-based methods for parallel preimplantation genetic testing for mitochondrial DNA disease and aneuploidy

OBJECTIVE

To validate and apply a strategy permitting parallel preimplantation genetic testing (PGT) for mitochondrial DNA (mtDNA) disease and aneuploidy (PGT-A).

DESIGN

Preclinical test validation and case reports.

SETTING

Fertility centers. Diagnostics laboratory.

PATIENTS

Four patients at risk of transmitting mtDNA disease caused by m.8993T>G (Patients A and B), m.10191T>G (Patient C), and m.3243A>G (Patient D). Patients A, B, and C had affected children. Patients A and D displayed somatic heteroplasmy for mtDNA mutations.

INTERVENTIONS

Embryo biopsy, genetic testing, and uterine transfer of embryos predicted to be euploid and mutation-free.

MAIN OUTCOME MEASURES

Test accuracy, treatment outcomes, and mutation segregation.

RESULTS

Accuracy of mtDNA mutation quantification was confirmed. The test was compatible with PGT-A, and half of the embryos tested were shown to be aneuploid (16/33). Mutations were detected in approximately 40% of embryo biopsies from Patients A and D (10/24) but in none from Patients B and C (n = 29). Patients B and C had healthy children following PGT and natural conception, respectively. The m.8993T>G mutation displayed skewed segregation, whereas m.3243A>G mutation levels were relatively low and potentially impacted embryo development.

CONCLUSIONS

Considering the high aneuploidy rate, strategies providing a combination of PGT for mtDNA disease and aneuploidy may be advantageous compared with approaches that consider only mtDNA. Heteroplasmic women had a higher incidence of affected embryos than those with undetectable somatic mutant mtDNA but were still able to produce mutation-free embryos. While not conclusive, the results are consistent with the existence of mutation-specific segregation mechanisms occurring during oogenesis and possibly embryogenesis.

Biallelic variants in two complex I genes cause abnormal splicing defects in probands with mild Leigh syndrome

Leigh syndrome is a genetically heterogeneous disorder resulting from deficient oxidative energy biogenesis. The syndrome is characterized by subacute episodic decompensations, transiently elevated lactate, and necrotizing brain lesions most often in the striatum and brainstem. Acute decompensation is often triggered by viral infections. Sequalae from repeated episodes leads to progressive neurological deterioration and death. The severity of Leigh syndrome varies widely, from a rapid demise in childhood to rare adult presentations. Although the causes of Leigh syndrome include genes affecting a variety of different pathways, more than 75 of them are nuclear or mitochondrial encoded genes involved in the assembly and catalytic activity of mitochondrial respiratory complex I. Here we report the detailed clinical and molecular phenotype of two adults with mild presentations of NDUFS3 and NDUFAF6-related Leigh Syndrome. Mitochondrial assays revealed slightly reduced complex I activity in one proband and normal complex I activity in the other. The proband with NDUFS3-related Leigh syndrome was mildly affected and lived into adulthood with novel biallelic variants causing aberrant mRNA splicing (NM_004551.2:c.419G > A; p.Arg140Gln; NM_004551.2:c.381 + 6 T > C). The proband with NDUFAF6-related Leigh syndrome had biallelic variants that cause defects in mRNA splicing (NM_152416.3:c.371 T > C; p.Ile124Thr; NM_152416.3:c.420 + 2_420 + 3insTA). The mild phenotypes of these two individuals may be attributed to some residual production of normal NDUFS3 and NDUFAF6 proteins by NDUFS3 and NDUFAF6 mRNA isoforms alongside mutant transcripts. Taken together, these cases reported herein suggest that splice-regulatory variants to complex I proteins could result in milder phenotypes.

A Chinese Family With Adult-Onset Leigh-Like Syndrome Caused by the Heteroplasmic m.10191T>C Mutation in the Mitochondrial MTND3 Gene

Leigh syndrome (LS) is a mitochondrial disease of infancy and early childhood, that is rarely seen in adults. The high degree of genetic and clinical heterogeneity makes LS a very complex syndrome. The clinical manifestations include neurological symptoms and various non-neurological symptoms, with different mutations differing in presentations and therapies. The m.10191T>C mutation in the mitochondrial DNA gene encoding in the respiratory chain complex I (CI) subunit of MTND3 results in the substitution of a highly conserved amino acid (p.Ser45Pro) within the ND3 protein, leading to CI dysfunction and causing a broad clinical spectrum of disorders that includes LS. Patients with the m.10191T>C mutation are rare in general, even more so in adults. In the present study, we report a family of patients with very rare adult-onset Leigh-like syndrome with the m.10191T>C mutation. The 24-year-old proband presented with seizures 6 years ago and developed refractory status epilepticus on admission. She had acute encephalopathy accompanied by lactic acidosis, symmetrical putamen and scattered cortical lesions. The video electroencephalogram suggested focal-onset seizures. She harbored the heteroplasmic m.10191T>C mutation in her blood and fibroblasts. Her aunt was diagnosed with mitochondrial disease at the age of 42, and had the heteroplasmic m.10191T>C mutation in her fibroblasts. Her aunt's son (cousin) died of respiratory failure at the age of 8, and we suspected he was also a case of LS. Furthermore, we reviewed the previously reported patients with the m.10191T>C mutation and summarized their characteristics. Recognizing the characteristics of these patients will help us improve the clinical understanding of LS or Leigh-like syndrome.

An Introduction to Pharmacotherapy for Inborn Errors of Metabolism

Inborn errors of metabolism comprise a wide array of diseases and complications in the pediatric patient. The rarity of these disorders limits the ability to conduct and review robust literature regarding the disease states, mechanisms of dysfunction, treatments, and outcomes. Often, treatment plans will be based on the pathophysiology associated with the disorder and theoretical agents that may be involved in the metabolic process. Medication therapies usually consist of natural or herbal products. Established efficacious pediatric doses for these products are difficult to find in tertiary resources, and adverse effects are routinely limited to single case reports. This review article attempts to summarize some of the more common inborn errors of metabolism in a manner that is applicable to pharmacists who will provide care for these patients.

MERRF Classification: Implications for Diagnosis and Clinical Trials

BACKGROUND

Given the etiologic heterogeneity of disease classification using clinical phenomenology, we employed contemporary criteria to classify variants associated with myoclonic epilepsy with ragged-red fibers (MERRF) syndrome and to assess the strength of evidence of gene-disease associations. Standardized approaches are used to clarify the definition of MERRF, which is essential for patient diagnosis, patient classification, and clinical trial design.

METHODS

Systematic literature and database search with application of standardized assessment of gene-disease relationships using modified Smith criteria and of variants reported to be associated with MERRF using modified Yarham criteria.

RESULTS

Review of available evidence supports a gene-disease association for two MT-tRNAs and for POLG. Using modified Smith criteria, definitive evidence of a MERRF gene-disease association is identified for MT-TK. Strong gene-disease evidence is present for MT-TL1 and POLG. Functional assays that directly associate variants with oxidative phosphorylation impairment were critical to mtDNA variant classification. In silico analysis was of limited utility to the assessment of individual MT-tRNA variants. With the use of contemporary classification criteria, several mtDNA variants previously reported as pathogenic or possibly pathogenic are reclassified as neutral variants.

CONCLUSIONS

MERRF is primarily an MT-TK disease, with pathogenic variants in this gene accounting for ~90% of MERRF patients. Although MERRF is phenotypically and genotypically heterogeneous, myoclonic epilepsy is the clinical feature that distinguishes MERRF from other categories of mitochondrial disorders. Given its low frequency in mitochondrial disorders, myoclonic epilepsy is not explained simply by an impairment of cellular energetics. Although MERRF phenocopies can occur in other genes, additional data are needed to establish a MERRF disease-gene association. This approach to MERRF emphasizes standardized classification rather than clinical phenomenology, thus improving patient diagnosis and clinical trial design.

Adult-onset Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis, and Stroke (MELAS)-like Encephalopathy Diagnosed Based on the Complete Sequencing of Mitochondrial DNA Extracted from Biopsied Muscle without any Myopathic Changes

The clinical features of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) are not uniform. We herein report a male patient with unusual MELAS-like encephalopathy who had been experiencing isolated recurrent stroke-like episodes since he was 33 years old without any particular family history. Despite an extensive investigation, he had no other signs suggestive of MELAS. Although the muscle pathology showed a normal appearance, a mitochondrial genome sequence analysis of the biopsied muscle revealed a heteroplasmic m.10158T>C mutation in the mitochondrial complex I subunit gene, MT-ND3. To prevented further deterioration of the higher brain function, the early diagnosis and treatment of mitochondrial stroke-like episodes is important.

The neuroimaging of Leigh syndrome: case series and review of the literature

Leigh syndrome by definition is (1) a neurodegenerative disease with variable symptoms, (2) caused by mitochondrial dysfunction from a hereditary genetic defect and (3) accompanied by bilateral central nervous system lesions. A genetic etiology is confirmed in approximately 50% of patients, with more than 60 identified mutations in the nuclear and mitochondrial genomes. Here we review the clinical features and imaging studies of Leigh syndrome and describe the neuroimaging findings in a cohort of 17 children with genetically confirmed Leigh syndrome. MR findings include lesions in the brainstem in 9 children (53%), basal ganglia in 13 (76%), thalami in 4 (24%) and dentate nuclei in 2 (12%), and global atrophy in 2 (12%). The brainstem lesions were most frequent in the midbrain and medulla oblongata. With follow-up an increased number of lesions from baseline was observed in 7 of 13 children, evolution of the initial lesion was seen in 6, and complete regression of the lesions was seen in 3. No cerebral white matter lesions were found in any of the 17 children. In concordance with the literature, we found that Leigh syndrome follows a similar pattern of bilateral, symmetrical basal ganglia or brainstem changes. Lesions in Leigh syndrome evolve over time and a lack of visible lesions does not exclude the diagnosis. Reversibility of lesions is seen in some patients, making the continued search for treatment and prevention a priority for clinicians and researchers.

Ischemic A/D transition of mitochondrial complex I and its role in ROS generation

Mitochondrial complex I (NADH:ubiquinone oxidoreductase) is a key enzyme in cellular energy metabolism and provides approximately 40% of the proton-motive force that is utilized during mitochondrial ATP production. The dysregulation of complex I function – either genetically, pharmacologically, or metabolically induced – has severe pathophysiological consequences that often involve an imbalance in the production of reactive oxygen species (ROS). Slow transition of the active (A) enzyme to the deactive, dormant (D) form takes place during ischemia in metabolically active organs such as the heart and brain. The reactivation of complex I occurs upon reoxygenation of ischemic tissue, a process that is usually accompanied by an increase in cellular ROS production. Complex I in the D-form serves as a protective mechanism preventing the oxidative burst upon reperfusion. Conversely, however, the D-form is more vulnerable to oxidative/nitrosative damage. Understanding the so-called active/deactive (A/D) transition may contribute to the development of new therapeutic interventions for conditions like stroke, cardiac infarction, and other ischemia-associated pathologies. In this review, we summarize current knowledge on the mechanism of A/D transition of mitochondrial complex I considering recently available structural data and site-specific labeling experiments. In addition, this review discusses in detail the impact of the A/D transition on ROS production by complex I and the S-nitrosation of a critical cysteine residue of subunit ND3 as a strategy to prevent oxidative damage and tissue damage during ischemia–reperfusion injury. This article is part of a Special Issue entitled Respiratory complex I, edited by Volker Zickermann and Ulrich Brandt.

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The current knowledge on active/deactive (A/D) transition of complex I is reviewed.

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The mechanism and driving force of the A/D conformational change are discussed.

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The A/D transition can affect ROS production and ischemia/reperfusion injury.

The genetics of Leigh syndrome and its implications for clinical practice and risk management

Leigh syndrome, also referred to as subacute necrotizing encephalomyelopathy, is a severe, early-onset neurodegenerative disorder that is relentlessly progressive and devastating to both the patient and the patient’s family. Attributed to the ultimate failure of the mitochondrial respiratory chain, once it starts, the disease often results in the regression of both mental and motor skills, leading to disability and rapid progression to death. It is a mitochondrial disorder with both phenotypic and genetic heterogeneity. The cause of death is most often respiratory failure, but there are a whole host of complications, including refractory seizures, that may further complicate morbidity and mortality. The symptoms may develop slowly or with rapid progression, usually associated with age of onset. Although the disease is usually diagnosed within the first year of life, it is important to note that recent studies reveal phenotypic heterogeneity, with some patients having evidence of in utero presentation and others having adult-onset symptoms.